12 replies to this topic

[Daze]

I want to fit one of those battery cut off things properly, I've had one loafing around in my garage for a long time. (one like this)

Quick question though, since mine is a cheaper version which doesn't include a resistor or anything then cutting out the battery cable itself, while the car is running, won't cut the car out.

So, I'm thinking about plumbing through one of the coil wires through the switch too. Will this work? So when I turn the switch off, the coil will loose it power and of course stop instantly, therefore stopping the car. Will this damage the coil though?

I'll also most probably be plumbing my electronic fuel pump through it too, for safety reasons.

Ta.

[Big_Adam]

If there's no connection from the bat in the boot to the engine then everything is dead. The resistor you talk of might be a fuse. This means all your stereo settings remain even if the bat cut off is used.

edit

oh wait. I get your. You want to be able to kill the engine when you like.......no idea then.

Edited by Big_Adam, 21 February 2007 - 03:42 PM.

[Daze]

Yep, exactly. I want to kill everything on one switch. I had an old switch wired in to the battery cable only (until it died), switching it off when the engine is running did nothing, everything remained working and running.

[milliemini]

Sorry to hijack the thread a little but I've got one of those switches too, want to install it in the cab under the dash to save opening up the boot all the time (only installing mine because I have a power drain somewhere and dont have time till mid march to sort it out so need to cut off power everytime I park the car up) wheres the best way to run the power cable from the battery to the coil as currently it goes from the boot under the car and then up into the engine bay. From the boot I can feed it thru a grommet in the back seats and under the carpets but where's best place to enter the engine bay? I'd rather not have to take the whole car apart or drill to many more holes!

[Daze]

I've done mine through the rear boot / bench along the floor then alongside the passenger footwell and up to the bulkhead, mine comes out right high on the drivers side, well out of the way of everything. Then again, its easy on my car - I don't have any sound insulation or carpet or anything!

[dklawson]

If you want to kill everything with one switch it's not necessarily safe or easy.

If your car has an alternator you shouldn't attempt to use a battery disconnect switch while the car is running. Doing so removes the load from an operating alternator which can damage its controls. When you read up on testing alternators this is one thing that you are warned NOT to do. I don't know what doing this on a generator equipped car would do but I've always assumed it would be equally bad.

[milliemini]

Lol, yeah mines fully kitted out atm carpets etc, dont have the garage or the driveway space atm to strip it all down, plus its supposed to be my daily driver but have hardly driven her since I brought her :'( Am moving house to bournemouth soon so looking for somewhere with a garage but really need to get her wired up and working asap.

[Daze]

dklawson - thanks for the reply.

You say it would damage the alternator, a fair point, but on race/rally cars they have these switches installed which I presume they use in case of an emergency to kill all power. They have red T-bar pull handles for the marshall's to pull which are mounted usually on the scuttle to kill power.

In case on an emergency on a race car, would this also mess-up the alternator? As its a race car, then it can be replaced of course.

Thanks again.

[Dan]

Lots of racers don't have alternators fitted. The races last long enough to run the car on a battery only without it running flat and so it is only extra weight. There are specific isolator units to isolate the battery and safely shut down an alternator when the button is pushed but without one it comes down to how the car is wired. Why are you doing this? I can't imagine it's a race car as you would never have passed scrutineering if the kill switch failed to shut down the car. Also as DK says it is very bad for your alternator to do this and also for your electronics. Without access to a 12v battery the alternator has no idea what 12v is and so the output voltage starts to drift wildly, it can kill all the electronics in your car.

milliemini, FIA type isolator switches are not the best thing to use as an isolator in a daily driver. They are cheaply made junk and fall apart easily. Daze seems to say above that his fell apart in less than a year and most racers will have to replace their switch during a season even though they are hardly used. If you use one every day it will soon become unreliable and you really don't want to be standing at the side of the road in the dark and rain waiting for the AA because your kill switch has failed you. They aren't designed for this. There are heavy duty switches available that can do this day in day out without worry but it's probably better to try to actually fix the car instead of hiding the problem.

[dklawson]

I hadn't considered the race car aspect of your question. The only such cars I'm routinely around are air-cooled VWs which race w/o a functional generator or alternator... they run only on the battery for short courses. There... we get away with the switch you showed in your picture link above.

You made me go googling. There are 4-post and 2-post battery switches. It appears that the 4-post switches are used for cars with alternators. I found a couple listed and one included a schematic for alternator equipped cars.
See:
http://longacreracin...text/4578PI.pdf
As I read over some of the descriptions, several of the 2-post switches mentioned them for use as disconnects when the car was not in use to prevent battery drainage.

Since I don't know how the contacts inside the switch shown in the above PDF are oriented, I can't speculate on how the use of the 4-post switches protects the alternator. However, what I'd like to remind you of regarding these switches on race cars is that they are there for the corner workers, not the driver or mechanic. They want a quick way to safely kill your car and they aren't worried about whether or not your alternator (if fitted) works after they have to turn that switch off.

[Daze]

Hi Dan, thanks for the reply.

I want to do this as a saftey feature more than anything, but also for the looks. I've rallied my Mini a few times, although since have given it up, but I intend to do a number of track days with it, and hill climbs and thought it would be a good thing to have one installed.

My Mini isn't my daily drive.

The FIA cut off switches are £30-£40, which is pricey, but they do do the trick, right? They are designed for cutting off a car completely from running, without using the ignition key? So with a red T-bar installed, its possible to kill the engine from outside the car?

[Dan]

FIA kill switches are the cheap plastic key switches like the one in your picture. As DK says, there are different types and you need the right one and to have your car wired the right way.

[fikus01]

definately need the 1 with the resistor otherwise as others have said it kills thr alternator and has the possibility of still running i believe!! otherwise its just a battery kill not an engine cut!